The present invention relates to a green glass which has advantages of high heat ray absorptivity, high ultraviolet absorptivity, high quality, and high productivity. It particularly relates to a glass having high visible light transmittance which has, a shade of green, and has a high heat ray absorption performance, and it more particularly relates to a green glass which is suitable for a window glass to be reinforced and installed in a vehicle.
A variety of glasses with ultraviolet/infrared absorptivity to be used as a vehicle windshield have been proposed with the view of preventing degradation of luxurious interior materials and reducing cooling load of the vehicle. In view of comfort of passengers and privacy protection, a glass having low visible light transmittance is preferably used for a rear window glass of a vehicle.
The front windshield of a vehicle is obligated to have a visible light transmittance higher than a specific level for enough visibility of a driver. A glass having high visible light transmittance and provided with ultraviolet and heat ray absorptivity has a greenish shade because the ends of its ultraviolet absorption range and infrared absorption range overlap the visible range.
Ultraviolet/infrared absorbent glasses having low to middle visible light transmittance, low ultraviolet transmittance and low total solar radiation transmittance have been disclosed in Japanese patent H10-114540A and H10-45425A. Since these ultraviolet/infrared absorbent glasses have high heat ray absorption characteristics, productivity of each glass in a glass melting furnace is low. Inside the melting furnace, a top of the glass is directly heated with flames, but the bottom of the glass material can not be sufficiently heated because a large part of heat rays directed at the surface of the glass material by the radiation of the flames are absorbed by the top of the glass material. It is thus difficult to melt the glass material in the melting furnace uniformly.
The glass material is necessarily maintained at a higher-than-normal degree of reduction in order to provide high heat ray absorption characteristics thereto. Therefore, a large amount of reducing agents, mainly including graphite powder, etc., can be added into the glass batch, but such agents are liable to cause unfused silica because the agents can exceedingly react with sulfate, mainly including sodium sulfate, etc., which is added to the glass batch as a refining agent.
In order to melt the glass material uniformly, at least one of the following processes can be adopted, such as: lowering the amount of the glass material below that for the ordinary operation; heating the bottom of the glass material by energizing electrodes inserted into the bottom of the furnace; and bubbling the glass material.
However, lowering the amount of the glass material below that for the ordinary operation causes decrease of the production capacity, thereby raising the production cost. Electrical heating by insertion of electrodes in the bottom of the furnace and bubbling the glass material require modification of the facilities. These processes can cause defects, such as: generation of a lot of defects such as bubbles in the glass depending upon the operating conditions, and result in significant decline of the production capacity.
The low transmittance glass of the present invention is composed of soda-lime-silica glass comprising 0.001 to 2 wt. % Li2O and, as colorant, 0.7 to 2.2 wt. % total iron oxide (T-Fe2O3) expressed as Fe2O3. The glass with a thickness between 2.1 mm and 6 mm has visible light transmittance (YA) of not greater than 65%, measured by using the CIE illuminant A, total solar radiation transmittance (TG) of not greater than 60%, and ultraviolet transmittance (Tuv) defined by ISO 9050 of not greater than 25%.
The low transmittance glass of the present invention has superior heat ray absorption properties, and it is improved in quality and productivity by including Li2O in its base glass composition so as to lower viscosity of the glass material, accelerating melt and homogenization of the glass material, and it also has superior capacity for reinforcement.
Since the glass material of the low transmittance glass of the present invention has low viscosity, melt and homogenization of the glass material are accelerated. The low transmittance glass is improved in quality and productivity, and is provided with low infrared transmittance.
Since when applied with reinforcement by air blast cooling, the low transmittance glass of the present invention obtains higher surface compression than that of conventional ones, it is superior in capacity for reinforcement. The low transmittance glass of the present invention has low visible light transmittance and low ultraviolet transmittance, so that it is suitable for a rear view window of a vehicle.
The ultraviolet/infrared absorbent green glass of the present invention is composed of soda-lime-silica glass comprising 0.001 to 2 wt. % Li2O and, as colorant, 0.4 to 2 wt. % total iron oxide (T-Fe2O3) expressed as Fe2O3 wherein FeO expressed as Fe2O3 is 15 to 60% of T-Fe2O3. The glass with a thickness between 2.1 mm and 6 mm has visible light transmittance (YA) of not less than 70%, measured by using the CIE illuminant A, and total solar radiation transmittance (TG) of not greater than 60%.
The ultraviolet/infrared absorbent green glass of the present invention has superior heat ray absorption properties, and it is improved in quality and productivity by including Li2O in its base glass composition so as to lower viscosity of the glass material, accelerating melt and homogenization of the glass material, and it also has superior capacity for reinforcement.
Since the glass material of the low ultraviolet/infrared absorbent green glass of the present invention has low viscosity, melt and homogenization of the glass material are accelerated. The green glass is improved in quality and productivity, and it is provided with low infrared transmittance. Since when applied with reinforcement by air blast cooling, the glass obtains higher surface compression than that of conventional ones, it is superior in capacity for reinforcement. The green glass has high visible light transmittance and low ultraviolet transmittance, so that it is suited for a window of a vehicle.